ATOMICSTRUCTURE Semester Chemistry Unit 2 KNOCKHARDY PUBLISHING

ATOMICATOMICSTRUCTURESTRUCTURE

Semester Chemistry Unit 2Semester Chemistry Unit 2

KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING

LecturePLUS Timberlake 2

Atomic Theory

Atoms are building blocks of elements

Similar atoms in each element

Different from atoms of other elements

Two or more different atoms bond in simple ratios

to form compounds

THE STRUCTURE OF ATOMSTHE STRUCTURE OF ATOMS

Atoms are the smallest particles of an element that have the properties of that element.

They consist of a number of fundamental particles,the most important are ...

LocationRelative charge

Relative mass (amu)

PROTON Nucleus +1 1

NEUTRON Nucleus 0 1

ELECTRON Electron shells -1 1/1837

MASS NUMBER AND ATOMIC NUMBERMASS NUMBER AND ATOMIC NUMBER

Atomic Number (Z) Number of protons in the nucleus of an atom

Mass Number (A) Sum of the protons and neutrons in the nucleus

Ions: Atom or electron that has lost or gained electrons.




Na23

11

Mass Number (A)PROTONS + NEUTRONS

Atomic Number (Z)PROTONS




Na23

11



THESE ALWAYS GO TOGETHER – ANYTHING WITH 11 PROTONS MUST

BE SODIUM




Na23

11






Na23

11



THERE WILL BE 12 NEUTRONS IN THE NUCLEUS

23 – 11 = 12




Na23

11




Protons Neutrons Electrons ChargeAtomic Number

Mass Number

Symbol

A 19 21 19

B 20 0 40

C + 11 23

D 6 6 0

E 92 0 235

F 6 13

G 16 2- 16

H 27Al3+


Protons Neutrons Electrons ChargeAtomic Number

Mass Number

Symbol

A 19 21 19 0 19 40 40K

B 20 20 20 0 20 40 40Ca

C 11 12 10 + 11 23 23Na+

D 6 6 6 0 6 12 12C

E 92 143 92 0 92 235 235U

F 6 7 6 0 6 13 13C

G 16 16 18 2- 16 32 32S2-

H 13 14 10 3+ 13 27 27Al3+

RELATIVE MASSESRELATIVE MASSES

Relative Atomic Mass (Ar)The mass of an atom relative to the 12C isotope having a value of 12.000

Ar = average mass per atom of an element x 12 mass of one atom of carbon-12

Relative Isotopic MassSimilar, but uses the mass of an isotope 238U

Relative Molecular Mass (Mr)Similar, but uses the mass of a molecule CO2, N2

Relative Formula MassUsed for any formula of a species or ion NaCl, OH¯


Atomic Mass

• Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.


Example of an Average Atomic Mass

• Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine.

• 35 x 75.5 = 26.4 • 100• 35.5

35.5 • 37 x 24.5 = 9.07

• 100

ISOTOPESISOTOPES

Definition Atoms with…

the same atomic number but different mass number orthe same number of protons but different numbers of neutrons.

Properties Chemical properties of isotopes are identicalPhysical properties (such as density) can differ


Isotopes

Atoms with the same number of protons, but

different numbers of neutrons.

Atoms of the same element (same atomic

number) with different mass numbers

Isotopes of chlorine

35Cl 37Cl17 17

chlorine - 35 chlorine - 37


Learning Check

• Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

• 12C 13C 14C• 6 6 6

• #p _______ _______ _______

• #n _______ _______ _______

• #e _______ _______ _______


Solution

• 12C 13C 14C• 6 6 6

• #p 6 6 6

• #n 6 7 8

• #e 6 6 6

ISOTOPESISOTOPES

Definition Atoms with…

the same atomic number but different mass number orthe same number of protons but different numbers of neutrons.

Properties Chemical properties of isotopes are identicalPhysical properties (such as density) can differ

Theory Atoms of the same element canhave different masses due to thevariation in the number of neutrons inthe nucleus. The atomic mass wasa consequence of the abundance ofeach type of isotope.

Protons Neutrons

1 H 1

1 0

2 H 1

1 1

3 H 1

1 2

ISOTOPES OF HYDROGEN

ISOTOPES - CALCULATIONSISOTOPES - CALCULATIONS

There are two common isotopes of chlorine. Calculate the average relative atomic mass of chlorine atoms

Protons Neutrons %

35 Cl 17

17 18 75

37 Cl 17 17 20 25



Method 1 Three out of every four atoms will be chlorine-35

Average = 35 + 35 + 35 + 37 = 35.5 4

Protons Neutrons %

35 Cl 17

17 18 75

37 Cl 17 17 20 25



Method 1 Three out of every four atoms will be chlorine-35

Average = 35 + 35 + 35 + 37 = 35.5 4

Method 2 Out of every 100 atoms 75 are 35Cl and 25 are 37Cl

Average = (75 x 35) + (25 x 37) = 35.5 100

Protons Neutrons %

35 Cl 17

17 18 75

37 Cl 17 17 20 25

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ATOMICSTRUCTURE Semester Chemistry Unit 2 KNOCKHARDY PUBLISHING